1. Field of the Invention
The present invention relates to an image forming apparatus having a display device usable as an input device.
2. Description of the Prior Art
With the recent progress in the microcomputer technology, general purpose input-output circuits are employed for control and display of copiers. For example in FIG. 1, a microcomputer 1 controls a general purpose input-output circuit 2 provided with three ports having eight terminals each, in which the port 1 for example is used for data input while the ports 2 and 3 are used for data output under the control of said microcomputer. The data input and output from and to said ports are conducted through a data bus.
Usually each port of such general purpose input-output circuit is assigned exclusively for data input or output. In certain instances, however, it is not possible to increase the number of such general purpose input-output circuits because of excessive cost or the large space required for mounting the components.